The invention relates generally to the field of illumination systems, and more specifically, to illumination systems using a wavelength-converting material, such as phosphor, located remotely from the light source, such as a light emitting diode.
Illumination systems are widely used to backlight display devices such as televisions, laptops, and Personal Digital Assistants (PDAs); to light up shelves in cabinets and kitchens; and for signage and contour lighting. An illumination system may include a light source that is coupled to an optical waveguide. The optical waveguide transmits the light produced by the light source to, for example, a display device.
Some existing illumination systems include Cold Cathode Fluorescent Lamps (CCFLs) as light sources. The light emitted by CCFLs is coupled into an optical waveguide, which transmits the light. However, CCFLs contain mercury, which may cause environmental hazards. Moreover, CCFLs are large in size and require high operational voltages.
Illumination systems that include Light Emitting Diodes (LEDs) as light sources are gaining in popularity. An example of the existing illumination systems that include LEDs as light sources are illumination systems that have a plurality of LEDs producing, for example, a white light or red, blue and green lights. The red, blue and green lights may be mixed to generate, for example, a substantially white light. Further, the existing illumination systems include packaging around the light sources to improve the efficiency of the existing illumination systems.
The packaging around the light sources increases the size of the existing illumination systems. In the existing illumination systems using LEDs, the red, blue and green lights have to be uniformly mixed to generate a substantially white light. However, it is difficult to achieve consistency in the spatial spectral distribution and brightness of the light in the existing illumination systems. Moreover, due to transmission losses, the efficiency of the existing illumination systems is low.